2018 Freightliner M2 body marker light issues

Hey guys, I've got a 2018 Freightliner M2 in the shop with body marker light issues. The headlights, running lights, and cab marker lights work, but the body marker lights quit working. How do you trouble shoot this particular issue? We are not a dealership shop so no manuals to get the steps I need in order to trouble shoot. As there is no fuse box per say, I'm not even sure where to start. Google is no help. I would really appreciate any advice. I edited this as I was seeing all kinds of views but no comments, revised a little, hoping this will help?! Thanks!

 

Never mind. After finding this file:///C:/Users/KCLOCKWIC2/Downloads/GHG%202014%20Electrical%20Guide.pdf
was able to trouble shoot better and found a bad ground.